1. Field of the Invention
The present invention relates generally to a performance prediction program and performance prediction system for a ground source heat pump system using ground heat, and more particularly to a performance prediction program and performance prediction system which is suitable for use in performance prediction for a ground source heat pump system which employs a plurality of buried tubes or U-shaped tube heat exchangers in a heat exchange system.
2. Description of the Related Art
Ground source heat pump systems, characterized by the use of renewable energy sources not affected by weather conditions and environmentally-friendly technology of no waste heat dissipation, have been attracting considerable attention. Under the circumstances, these systems are increasingly used, primarily in Europe and the United States. A conventional ground source heat pump system, as disclosed in Japanese Unexamined Patent Publication No. 2001-289533, comprises a U-shaped buried tube placed into a borehole in the ground as a heat exchanger and a heat pump mounted on the ground, in which an antifreeze is circulated through the buried tube, to provide efficient heating and cooling by heat absorption and discharge with the ground.
Preferably, for installing the above mentioned ground source heat pump system with high installation costs, the heat exchanger has the dimensions, number of units and layout based on an individual and specific design to achieve high system performance, energy-saving and low-cost advantages. This conventional ground source heat pump system is prone, however, to several shortcomings. First, since conventional researches focus exclusively on the development of system structure to make the ground source heat pump more efficient, system evaluation techniques, in which performance for a proposed system can be predicted to provide a comprehensive equipment evaluation and thus improve system design, has not been established. Due to this shortcoming, conventional construction approaches have a problem of setting a higher safety factor, sorely based on previous construction experiences for system design and works execution.
Meanwhile, performance prediction for a ground source heat pump system requires a comprehensive equipment evaluation based on analytical data, such as system efficiency, power consumption, underground temperature, amount of carbon-dioxide emission, running costs and life cycle. There is another difficulty in obtaining other basic data for such a comprehensive evaluation, e.g. underground temperature and its change. In a more specific manner, the use of a large number of buried tubes in a ground source heat pump system, aimed at promoting heat absorption and discharge between heat exchangers and the ground, will significantly affect underground temperature patterns by a long-term heat transfer, thereby causing a difficult calculation on its underground temperature change. Moreover, the impact of a plurality of buried tubes, in view of the alignment thereof at different intervals, on soil temperature change, must be examined as well.
For example, the use of a steel-pipe well type heat exchanger can facilitate heat transfer analysis due to a property thereof as a hollow circular cylinder. But, the above mentioned ground source heat pump system employs various shapes of heat exchangers such as single U-shaped tube and double U-shaped tube, thus it is hard to precisely calculate thermal resistance required for calculating system efficiency.